Caspase-1, a cysteine protease, is critical for the processing and secretion of IL-1( and IL-18, two pro- inflammatory cytokines that play an important role in host defense, sepsis, and the pathogenesis of several inflammatory diseases. The activation of caspase-1 is controlled by members of the intracellular NOD-like receptor (NLR) family including NLRC4 and NLRP3. Recent work from several laboratories indicate that NLRC4 and NLRP3 regulate caspase-1 activation through the assembly of a molecular platform termed "the inflammasome" that includes the adaptor ASC and caspase-1. We have obtained evidence that NLRC4 senses bacterial flagellin that is introduced into the host cytosol via membrane pores formed by bacterial type III or IV secretion systems. In contrast, NLRP3 responds to bacterial pore-forming toxins, ATP and particulate matter in macrophages stimulated with microbial molecules or endogenous cytokines. Our knowledge about the inflammasome is limited and primarily derived from cellular and animals models of systemic inflammation. We have obtained Preliminary Results supporting an important role for the inflammasome in intestinal inflammation driven by enteric infection. The goal of this proposal is to provide a better understanding of the mechanisms that govern the activation of the inflammasome in intestinal phagocytes and the role of NLRC4 and NLRP3 in the response to clinically relevant intestinal bacteria. Biochemical, genetic, and cellular approaches will be employed to study the function and activation of the inflammasome in intestinal immunity using Salmonella and Crohn's disease-associated invasive-adherent E. coli. Given the important role of IL-1( in immunity and inflammatory disease, understanding of the mechanism involved in caspase-1 activation and IL-1( production in the intestine is expected to have a significant impact in the medical field PUBLIC HEALTH RELEVANCE: The inflammasomes play a critical in host defense and contributes to inflammatory responses through the regulation of caspase-1 activation and IL-1(/IL-18 secretion. We find that the NLRC4 and NLRP3 inflammasomes are important for the detection of intestinal bacteria pathogens and host defense in the intestine. The main goal of this proposal is to understand the regulation, activation and function of the inflammasomes in response to clinically relevant Salmonella and adherent-invasive E. coli, two enteric bacterial pathogens. These studies may lead to better understanding of mechanisms that control host defense against human pathogens and the pathogenesis of inflammatory disease in the intestine.